1. Field of the Invention
This invention relates to a method and apparatus for rapidly drying a water laden porous or foraminous structure by passing heated air through the structure to remove the water.
2. Description of the Prior Art
Many foamed structures such as mattresses are made essentially dry from forms of polyurethane or from other polymers having little amounts of water present during their formation. As a result there has not been any drying problem when making these conventional products which would require removing large amounts of water.
Recently, hydrophilic polyurea-polyurethanes have been developed which are foamed by using large amounts of water. One example of this foam system is disclosed in Wood et al U.S. Pat. No. 4,137,200. These foams have many utilities. However, most of the uses of the foam require a final drying step to remove the water.
In addition, there has been concern about increasing the fire resistance of polyurethane foams to be used in cushions, mattresses and other similar fire susceptible foam structures. One way to make a more fire resistant foamed product is to mix this hydrophilic polyurea polyurethane prepolymer in about an equal amount with an aqueous slurry containing fire retardant additives. Examples of this system and useful additives are disclosed in U.S. Pat. Nos. 3,987,372 to Kehr et al, 4,066,578 to Murch et al, 4,165,411 to Marans et al and 4,230,822 to Murch et al. Again, the resulting foamed products contain a large amount of water which has been used to deliver the additives into the foam network. Similar structures made from latex-derived foams also have large amounts of water.
The problem presented is how to remove the water from these structures in a rapid, economical manner. One conventional method of drying these latex and polyurea-polyurethane foams involves placing them in a heated oven with air circulating around the foam pieces. Alternatively, the structures such as mattresses can be placed in a heated room for 24 to 72 hours or more to dry them out. These conventional techniques, however, require relatively long periods of time for drying which restricts the factory throughput when making each day many large structures such as mattresses.
Foam structures have also been dried by using radio frequency drying apparatus. However, for large foamed structures this technique is expensive in view of the substantial capital cost to purchase this equipment.